ROAMOPS Working Group Bernard Aboba INTERNET-DRAFT Microsoft Category: Standards Track Mark A. Beadles WorldCom Advanced Networks 7 November 1998 The Network Access Identifier 1. Status of this Memo This document is an Internet-Draft. Internet-Drafts are working docu- ments of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute work- ing documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference mate- rial or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.ietf.org (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). The distribution of this memo is unlimited. It is filed as and expires May 1, 1999. Please send com- ments to the authors. 2. Copyright Notice Copyright (C) The Internet Society (1998). All Rights Reserved. 3. Abstract In order to enhance the interoperability of roaming and tunneling ser- vices, it is desirable to have a standardized method for identifying users. This document proposes syntax for the Network Access Identi- fier (NAI), the userID submitted by the client during PPP authentica- tion. It is expected that this will be of interest for support of roaming as well as tunneling. "Roaming capability" may be loosely defined as the ability to use any one of multiple Internet service providers (ISPs), while maintaining a formal, customer-vendor rela- tionship with only one. Examples of where roaming capabilities might be required include ISP "confederations" and ISP-provided corporate network access support. Aboba & Beadles Standards Track [Page 1] INTERNET-DRAFT The Network Access Identifier 7 November 1998 4. Introduction Considerable interest has arisen recently in a set of features that fit within the general category of "roaming capability" for dialup Internet users. Interested parties have included: Regional Internet Service Providers (ISPs) operating within a particular state or province, looking to combine their efforts with those of other regional providers to offer dialup service over a wider area. National ISPs wishing to combine their operations with those of one or more ISPs in another nation to offer more comprehensive dialup service in a group of countries or on a continent. Businesses desiring to offer their employees a comprehensive package of dialup services on a global basis. Those services may include Internet access as well as secure access to corporate intranets via a Virtual Private Network (VPN), enabled by tunnel- ing protocols such as PPTP, L2F, L2TP, and IPSEC tunnel mode. In order to enhance the interoperability of roaming and tunneling ser- vices, it is desirable to have a standardized method for identifying users. This document proposes syntax for the Network Access Identi- fier (NAI). Examples of implementations that use the NAI, and descriptions of its semantics, can be found in [1]. 4.1. Terminology This document frequently uses the following terms: Network Access Identifier The Network Access Identifier (NAI) is the userID submitted by the client during PPP authentication. In roaming, the purpose of the NAI is to identify the user as well as to assist in the routing of the authentication request. Please note that the NAI may not necessarily be the same as the user's e-mail address or the userID submitted in an applica- tion layer authentication. Network Access Server The Network Access Server (NAS) is the device that clients dial in order to get access to the network. In PPTP termi- nology this is referred to as the PPTP Access Concentrator (PAC), and in L2TP terminology, it is referred to as the L2TP Access Concentrator (LAC). Roaming Capability Roaming capability can be loosely defined as the ability to use any one of multiple Internet service providers (ISPs), while maintaining a formal, customer-vendor relationship with only one. Examples of cases where roaming capability might be required include ISP "confederations" and ISP- Aboba & Beadles Standards Track [Page 2] INTERNET-DRAFT The Network Access Identifier 7 November 1998 provided corporate network access support. Tunneling Service A tunneling service is any network service enabled by tun- neling protocols such as PPTP, L2F, L2TP, and IPSEC tunnel mode. One example of a tunneling service is secure access to corporate intranets via a Virtual Private Network (VPN). 4.2. Requirements language In this document, the key words "MAY", "MUST, "MUST NOT", "optional", "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as described in [9]. 4.3. Purpose As described in [1], there are now a number of services implementing dialup roaming, and the number of Internet Service Providers involved in roaming consortia is increasing rapidly. In order to be able to offer roaming capability, one of the require- ments is to be able to identify the user's home authentication server. For use in roaming, this function is accomplished via the Network Access Identifier (NAI) submitted by the user to the NAS in the ini- tial PPP authentication. It is also expected that NASes will use the NAI as part of the process of opening a new tunnel, in order to deter- mine the tunnel endpoint. 4.4. Notes for Implementors As proposed in this document, the Network Access Identifier is of the form user@realm. Please note that while the user portion of the NAI conforms to the BNF described in [5], the BNF of the realm portion allows the realm to begin with a digit, which is not permitted by the BNF described in [4]. This change was made to reflect current prac- tice; although not permitted by the BNF described in [4], FQDNs such as 3com.com are commonly used, and accepted by current software. Please note that NAS vendors may need to modify their devices so as to support the NAI as described in this document. Devices handling NAIs MUST support an NAI length of at least 72 octets. 5. Formal definition of the NAI The grammar for the NAI is given below, described in ABNF as docu- mented in [7]. The grammar for the username is taken from [5], and the grammar for the realm is an updated version of [4]. nai = username / ( username "@" realm ) Aboba & Beadles Standards Track [Page 3] INTERNET-DRAFT The Network Access Identifier 7 November 1998 username = dot-string realm = realm "." label label = let-dig * (ldh-str) ldh-str = *( Alpha / Digit / "-" ) let-dig dot-string = string / ( dot-string "." string ) string = char / ( string char ) char = c / ( "\" x ) let-dig = Alpha / Digit Alpha = %x41-5A / %x61-7A ; A-Z / a-z Digit = %x30-39 ;0-9 c = < any one of the 128 ASCII characters, but not any special or SP > x = %x00-7F ; all 127 ASCII characters, no exception SP = %x20 ; Space character special = "<" / ">" / "(" / ")" / "[" / "]" / "\" / "." / "," / ";" / ":" / "@" / %x22 / Ctl Ctl = %x00-1F / %x7F ; the control characters (ASCII codes 0 through 31 ; inclusive and 127) Examples of valid Network Access Identifiers include: fred@3com.com fred@foo-9.com fred_smith@big-co.com fred=?#$&*+-/^smith@bigco.com fred@bigco.com nancy@eng.bigu.edu eng!nancy@bigu.edu eng%nancy@bigu.edu Examples of invalid Network Access Identifiers include: fred@foo fred@foo_9.com @howard.edu fred@bigco.com@smallco.com eng:nancy@bigu.edu eng;nancy@bigu.edu Aboba & Beadles Standards Track [Page 4] INTERNET-DRAFT The Network Access Identifier 7 November 1998 @bigu.edu 6. References [1] Aboba, B., Lu J., Alsop J.,Ding J., and W. Wang, "Review of Roam- ing Implementations", RFC 2194, September 1997. [2] Rigney C., Rubens A., Simpson W., and S. Willens, "Remote Authen- tication Dial In User Service (RADIUS)", RFC 2138, April 1997. [3] Rigney C., "RADIUS Accounting", RFC 2139, April 1997. [4] Mockapetris, P., "Domain Names - Implementation and Specifica- tion", RFC 1035, November 1987. [5] Postel, J., "Simple Mail Transfer Protocol", RFC 821, August 1982. [6] Gulbrandsen A., and P. Vixie, "A DNS RR for specifying the loca- tion of services (DNS SRV)", RFC 2052, October 1996. [7] Crocker, D., and P. Overrell, "Augmented BNF for Syntax Specifica- tions: ABNF", RFC 2234, November 1997. [8] Atkinson, R., "Security Architecture for the Internet Protocol", RFC 1825, August 1995. [9] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 7. Security Considerations Since an NAI reveals the home affiliation of a user, it may assist an attacker in further probing the username space. Typically this problem is of most concern in protocols which transmit the user name in clear- text across the Internet, such as in RADIUS, described in [2] and [3]. In order to prevent snooping of the user name, protocols may use con- fidentiality services provided by IPSEC, described in [8]. 8. IANA Considerations This document defines a new namespace that will need to be adminis- tered, namely the NAI realm namespace. In order to to avoid creating any new administrative procedures, administration of the NAI realm namespace will piggyback on the administration of the DNS namespace. NAI realm names are required to be unique and the rights to use a given NAI realm for roaming purposes are obtained coincident with acquiring the rights to use a particular fully qualified domain name (FQDN). Those wishing to use an NAI realm name should first acquire the rights to use the corresponding FQDN. Using an NAI realm without ownership of the corresponding FQDN creates the possibility of Aboba & Beadles Standards Track [Page 5] INTERNET-DRAFT The Network Access Identifier 7 November 1998 conflict and therefore is to be discouraged. Note that the use of an FQDN as the realm name does not imply use of the DNS for location of the authentication server or for authentica- tion routing. Since to date roaming has been implemented on a rela- tively small scale, existing implementations typically handle location of authentication servers within a domain and perform authentication routing based on local knowledge expressed in proxy configuration files. The implementations described in [1] have not found a need for use of DNS for location of the authentication server within a domain, although this can be accomplished via use of the DNS SRV record, described in [6]. Similarly, existing implementations have not found a need for dynamic routing protocols, or propagation of global routing information. Note also that there is no requirement that the NAI rep- resent a valid email address. 9. Acknowledgements Thanks to Glen Zorn of Microsoft for many useful discussions of this problem space. 10. Authors' Addresses Bernard Aboba Microsoft Corporation One Microsoft Way Redmond, WA 98052 Phone: 425-936-6605 EMail: bernarda@microsoft.com Mark A. Beadles WorldCom Advanced Networks 5000 Britton Rd. Hilliard, OH 43026 Phone: 614-723-1941 EMail: mbeadles@wcom.net 11. Full Copyright Statement Copyright (C) The Internet Society (1997). All Rights Reserved. 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